RENIX problems? Under 10 MPG!!!

My 89 Chero 4.0 auto runs rough. Gas milesage is under 10 mpg, lots of unburned gas / fumes. If I unplug any injector but # 2 engine will lose rpms(2 ohms to ground and 2 ohms to ecu terminal), ran new wire, terminal to ecu, new ground. tried 2 new plugs, plenty of blue spark. New sp wires. No vacuum leaks, adj tps, new coolant sensor, 2nd O2, 2nd ecu. Any ideas? I downloaded the RENIX manual and tested everything. Where are all the computer / fuel injection grounds located? Started stalling 4x today, starts up with WOT, and lots of smoke from unbuned gas.

I'd have to look to confirm, but I'm thinking all the injectors go to a common ground. Since you say that "pulling all but the #2 injector" changes things, have you tried checking for function at the #2 injector plug? This can be done with a "noid light," which should be available for $5 or so at a well-stocked parts house. Unplug the connector from the injector, plug in the light, and see if it flashes when the engine runs or cranks.

Since you're saying you're getting a lot of fumes and fuel out the tailpipe, I'm thinking that you're running on five cylinders. This probably won't account for all your lost mileage (nearly 50%!) but should account for some of it.

If the injector isn't firing, you'll probably have to send your ECU out to be remanned. I've heard of only two RENIX computers blowing out - both of them lost injector drivers. One of these days, I'll see what it takes to replace them...

If you PM or email me (dragonland2001 AT yahoo DOT com,) I can dig a little deeper and give you an idea where to look.

5-90

DRB II. Some dealers might still have one. I am sure it tells you if the sensors are working. Have you tuned it up recently? Cap, rotor, wires? New spark plugs? I got my tune up kit from Summit Racing today.

It doesn't take a computer to troubleshoot an XJ. You forget how things were done before computers told us everything. Pull the plugs and take a look. From that you can tell if #2 is running too lean or rich. It may not be an injector problem, you may have a bad plug, bad wire, arcing distributor cap, burnt valve, a hole in a piston, shot rings, any number of things. First check the plug. Maybe do a compression test while the plug is out. Make sure the plug is firing.

Losing one cylinder can take your mileage down that far. That cylinder will be a significant drag on the other 5 cylinders.

Ok - I just couldn't see losing 1/6 of your engine causing 1/2 drop in mileage - but I'm in "CNC Mode" right now... Damn G-code.

Still, you don't need a computer to troubleshoot - that's why I like RENIX. I can check everything out with a meter - I just want a code reader to get realtime data when I'm working on a knotty problem...

5-90

Ain't G code fun :laugh3:

I switched injectors around- 2 sets 4 times #2 never has any effect 2nd ecu today NO effect. A local mechanic had 2 jeep adapters for his SNAPON mt2500 but couldn't find either to test. This reallly sux as I drive about 80 miles a day for work, x -10mpg in Orlando traffic.

Bad MAP sensor.

My first place to look would be a plugged CAT, if your CAT was working it would be shooting flames burning that much fuel.

I dont like to just throw ideas out there, but try unplugging the TPS from the throttle if that changes anything, this seems to me like the TPS has gone south.

I unplugged the injector for cyl #2 and drove for work today (upto 100 mi a day) it ran better- lots less smoke AND fumes I assumed other cylinders were sucking gas from #2 not getting gas., so I thought must be intake valve problem. YES it was, rocker arm bolt broke, bracket between int and ex rockers retained broken rocker so pushrod/lifter didn't let loose, but valve, retainer, rocker are shot. For this amount of damage I can't believe how quiet the motor is! EZ out broke in head, and could'nt remove. OH WELL,I'll picked up a head tomorrow as this head is now f#@&$ after trying to remove the
EZ OUT. $24.95 for a head, Daytona Speedway UPULLIT has complete engines on sale this weekend for $74.95, MAN I LOVE THAT PLACE! Something tells me I'll be losing a vibration now too!